Lithium secondary battery

ABSTRACT

Provided is a novel lithium secondary battery including a positive electrode including a compound capable of occluding and discharging lithium, a negative electrode composed mainly of a carbon material which includes a graphite as an only or as a principal component, a separator between the positive electrode and the negative electrode; and an electrolyte solution of an electrolyte solute dissolved in a solvent including at least one specific cyclic compound. 
     The lithium secondary battery has a large capacity, small self-discharge rate and excellent cycle characteristics and high charge-discharge efficiency.

This application is a division of application Ser. No. 08/188,609, filedJan. 24, 1994, now U.S. Pat. No. 5,686,138. Application Ser. No.08/188,609 is a continuation-in-part application of prior applicationSer. No. 08/048,063, filed Apr. 19, 1993, now abandoned, which is acontinuation of application Ser. No. 07/850,486, filed Mar. 12, 1992,now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a lithium secondary battery, and morespecifically to improvement of a carbon material for a negativeelectrode of a lithium secondary battery, or to improvement of both anegative electrode and an electrolyte solution of a lithium secondarybattery.

2. Description of the Prior Art

In recent years, carbon materials have been studied, instead ofconventional lithium alloys, for the use of negative electrode materialfor lithium secondary batteries because 1 they have high flexibility and2 they do not cause mossy-shaped lithium to precipitate by electrolysis.

The carbon material that has principally been studied for this purposeis coke (see U.S. Pat. No. 4,725,422), and graphite has hardly beenstudied. For instance, U.S. Pat. No. 4,725,422 discloses a secondarybattery comprising for the negative electrode a carbon material havingthe spacing of (002) planes, d₀₀₂, of at least 3.37 Å and thecrystallite size in the direction of c axis, Lc of not more than 220 Å.The above carbon material is a kind of coke.

Coke, however, hardly provides large-capacity batteries, since theamount of lithium introduced with coke negative electrode is notsufficiently large.

To the best of the knowledge of the present inventors, the literaturesthat propose a secondary battery having a negative electrode comprisinggraphite are only U.S. Pat. No. 4,423,125 and U.S. Pat. No. 5,130,211.

The above U.S. Pat. No. 4,423,125 discloses a secondary batterycomprising for the negative electrode a carbon material having occludedlithium as an active material and as an electrolyte solution a solutionof an electrolyte solute of LiAsF₆ dissolved in a solvent of1,3-dioxolane. According to the USP, a secondary battery havingexcellent cycle characteristics can then be obtained.

The above known secondary battery is, however, inferior in many featuressuch as capacity per unit weight of graphite (mAh/g), initial charge anddischarge efficiency (%), battery capacity (mAh), self-discharge rate(%/month) and charge and discharge efficiency (%), not to mention cyclecharacteristics (cycle life), as shown by the data for the "conventionalbattery" in the later-described Examples. The battery therefore is notsufficiently satisfactory for practical purposes.

This is considered to be due to polymerization of 1,3-dioxolane in thenegative electrode side (reduction side).

The above U.S. Pat. No. 5,130,211 discloses a secondary batterycomprising for the negative electrode a carbon material having a degreeof graphitization greater than about 0.40 Å, i.e. the spacing of (002)planes, d₀₀₂ smaller than about 3.412 Å. The above known secondarybattery , however, is not necessarily excellent in the featuresmentioned above.

SUMMARY OF THE INVENTION

Accordingly, an object of the invention is to provide a lithiumsecondary battery having a negative electrode comprising specifiedgraphite, having a large capacity, small self-discharge rate andexcellent cycle characteristics and still having high initial charge anddischarge efficiency.

The above object can be achieved by providing a lithium secondarybattery comprising:

a negative electrode composed mainly of a carbon material whichcomprises, as an only or as a principal component, a graphite having:

(a) a d-value of the lattice plane (002) obtained by the X-raydiffraction method thereof of 3.354 to 3.370 and

(b) a crystallite size in the c-axis direction obtained by the X-raydiffraction method thereof of at least 200 Å,

a positive electrode composed mainly of a compound capable of occludingand discharging lithium and which is not the graphite used for thenegative electrode;

a separator between said positive electrode and said negative electrode;and

an electrolyte solution of an electrolyte solute dissolved in a solvent.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention and many of the attendantadvantages thereof will be readily obtained as the same become betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, wherein:

FIG. 1 is a graph showing the charge-discharge cycle characteristics ofthe battery of the present invention and a comparison battery (cokenegative electrode);

FIG. 2 is a sectional view of a cylindrical battery;

FIG. 3 is a graph showing the charge-discharge characteristics of thebatteries BA1 through BA3 of the present invention and the comparisonbattery BC1;

FIG. 4 is a graph showing the charge-discharge characteristics of thebattery BA1 of the present invention;

FIG. 5 is a graph showing the charge-discharge characteristics of thebattery BA2 of the present invention;

FIG. 6 is a graph showing the cycle characteristics of the batteries BA1and BA2 of the present invention and the comparison battery BC1;

FIG. 7 is a graph showing the cycle characteristics of the battery BA5of the present invention;

FIG. 8 is a graph showing the charge-discharge characteristics of thebatteries BA6 of the present invention, a comparison battery BC2 and aconventional battery;

FIG. 9 is a graph showing the relationship between the d₀₀₂ value of acarbon material and the discharge capacity of the battery utilizing anegative electrode of the carbon material;

FIG. 10 is a graph showing the relationship between the true density ofa carbon material and the discharge capacity of the battery;

FIG. 11 is a graph showing the relationship between the average particlediameter of a carbon material and the discharge capacity of the battery;

FIG. 12 is a graph showing the relationship between the specific surfacearea of a carbon material and the discharge capacity of the battery;

FIG. 13 is a graph showing the relationship between the Lc value of acarbon material and the discharge capacity of the battery; and

FIGS. 14 through 22 are graphs showing the relationships between themixing ratio by volume of components in various mixed solvents and thebattery capacity.

FIG. 23 is a graph showing the relationship between the Lc value of eachof the graphites having a d-value of less than 3.355 and the dischargecapacity and initial charge-discharge efficiency;

FIG. 24 is a graph showing the relationship between the Lc value of eachof the graphites having a d-value of 3.355 or more and less than 3.360and the discharge capacity and initial charge-discharge efficiency;

FIG. 25 is a graph showing the relationship between the Lc value of eachof the graphites having a d-value of 3.360 or more and less than 3.365and the discharge capacity and initial charge-discharge efficiency;

FIG. 26 is a graph showing the relationship between the Lc value of eachof the graphites having a d-value of 3.365 or more and less than 3.370and the discharge capacity and initial charge-discharge efficiency;

FIG. 27 is a graph showing the relationship between the Lc value of eachof the graphites having a d-value of 3.370 and the discharge capacityand initial charge-discharge efficiency;

FIG. 28 is a graph showing the relationship between the Lc value of eachof the graphites having a d-value of 3.380 or more and less than 3.385and the discharge capacity and initial charge-discharge efficiency;

FIG. 29 is a graph showing the relationship between the Lc value of eachof the graphites having a d-value of 3.385 or more and less than 3.390and the discharge capacity and initial charge-discharge efficiency;

FIG. 30 is a graph showing the relationship between the Lc value of eachof the graphites having a d-value of 3.390 or more and less than 3.395and the discharge capacity and initial charge-discharge efficiency;

FIG. 31 is a graph showing the relationship between the Lc value of eachof the graphites having a d-value of 3.395 or more and less than 3.400and the discharge capacity and initial charge-discharge efficiency;

FIG. 32 is a graph showing the relationship between the d-value and thedischarge capacity, with the Lc being at least 200 Å;

FIG. 33 is a graph showing the relationship between the d-value and theinitial charge-discharge efficiency, with the Lc being at least 200 Å;

FIG. 34 is a graph showing the relationship between the d-value and thedischarge capacity, with the Lc being less than 200 Å; and

FIG. 35 is a graph showing the relationship between the d-value and theinitial charge-discharge efficiency, with the Lc being less than 200 Å.

FIG. 36 is a graph showing the relationship between the BET specificsurface area and the discharge capacity and initial charge-dischargeefficiency.

FIG. 37 is a graph showing the relationship between the average particlediameter and the discharge capacity and initial charge-dischargeefficiency.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Examples of the compound that constitutes the positive electrodematerial in the present invention and is capable of occluding anddischarging lithium are, as inorganic compounds, oxides having what isknown as tunnel-shaped pores, such as MnO₂, TiO₂ and V₂ O₅, and metalchalcogenides such as TiS₂ and MoS₂ having laminar structure, amongwhich preferred are composite oxides represented by the formula Li_(x)MO₂ or Li , M₂ O₄, wherein M is a transition element and 0≦x≦1 and0≦y≦2. Concrete examples of the composite oxides are LiCoO₂, LiMnO₂,LiNiO₂, LiCrO₂ and LiMn₂ O₄.

The positive electrode material is kneaded with a conductor such asacetylene black or carbon black and a binder such aspolytetrafluoroethylene (PTFE) or polyvinylidene fluoride (PVdF), andthe obtained mixture is used as a material for preparing the positiveelectrode.

At this time, among the above conductive polymers and dopant-containingconductive polymers, those having high conductivity may be kneaded onlywith a binder, without incorporation of any conductor.

The graphite used as an only or a principal component of the carbonmaterial of the negative electrode of the lithium secondary battery inthe present invention has the following properties 1 and 2.

1 a d-value (d₀₀₂) of the lattice plane (002) obtained by the X-raydiffraction method thereof of 3.354 to 3.370 (unit: Å); and

2 a crystallite size (Lc) in the c-axis direction obtained by the X-raydiffraction method thereof of at least 200 Å.

The use of a graphite having the above properties 1 and 2 results in alithium secondary battery having a large discharge capacity and highinitial charge-discharge efficiency. If the graphite used as theprincipal component of the carbon material of the negative electrode ofthe lithium secondary battery of the present invention has a d-value andan Lc falling outside of the above range, the discharge capacity andinitial charge-discharge efficiency will be significantly lower.

When a graphite further having one of the following properties 3˜5 inaddition to the above properties 1 and 2 is used, better batterycharacteristics are obtained, as shown in the later-described Examples.

3 an average particle diameter of 1 to 30 μm;

4 a specific surface area of 0.5 to 50 m² /g; and

5 a true density of 1.9 to 2.25 g/cm³.

Further desirable properties of the graphite used in the presentinvention are as follows. The crystallite size in the a-axis directionobtained by the X-ray diffraction method thereof is at least 200 Å; theatomic ratio of H/C is not more than 0.1 and the G-value (1360 cm⁻¹/1590 cm⁻¹) in Raman spectroscopic analysis is at least 0.05.

Any kind of graphite can be suitably used in the present invention,whether it be natural graphite, artificial graphite or kish as long asit has the properties required of the graphite as explained above. Here,kish is a carbon material having higher crystallinity than naturalgraphite and formed, when in iron mills iron is melted in the blastfurnace at a temperature of at least 2,000° C., by sublimation and thesucceeding deposition onto the furnace wall and recrystallization of thecarbon contained in the iron. Further these graphites may as required beused in combination. The artificial graphite herein includesgraphite-based substances formed by processing or modifying graphite,such as swollen graphite.

Examples of natural graphite are Sri Lanka graphite, Madagascargraphite, Korea flake-graphite, Korea earth-graphite and China graphite,and an example of artificial graphite is coke-origin-graphite.

Table 1 shows the d-values of the lattice plane (002) and Lc's obtainedby the X-ray diffraction method of the above natural graphites andartificial coke-origin-graphite.

                  TABLE 1    ______________________________________                  Lattice constant                           Crystallite                  d(002) (Å)                           size,Lc(Å)    ______________________________________    Natural graphite    Sri Lanka       3.358      >1,000    Madagascar      3.359      >1,000    Korea (flake)   3.360      >1,000    Korea (earth)   3.365      230    China           3.354      >1,000    Artificial coke-                    3.364      350    origin-graphite    ______________________________________

Examples of commercially available natural graphite used in the presentinvention are "NG-2", "NG-2L", "NG-4", "NG-4L", "NG-7", "NG-7L","NG-10", "NG-10L", "NG-12", "NG-12L", "NG-14" and "NG-14L", which arehigh-purity graphite having a purity of at least 99% and made by TheKansai Coke and Chemicals Co., Ltd.; "CX-3000", "FBF", "BF", "CBR","SSC-3000", "SSC-600", "SSC-3", "SSC", "CX-600", "CPF-8", "CPF-3","CPB-6S", "CPB", "96E", "96L"), "96L-3", "90L-", "CPC", "S-87" and"K-3", (the foregoing are flake-graphites) and "S-3" and "AP-6", (theforegoing are earth-graphites) which are made by Chuetsu Graphite WorksCo., Ltd.; "CSSP", "CSPE", "CSP" and "Super-CP", (the foregoing areflake-graphites), and "ACP-1000", "ACP", "ACB-150", "SP-5", "SP-5L","SP-10", "SP-10L", "SP-20", "SP-20L" and "HOP" (the foregoing arehigh-purity graphite having a purity of at least 97.5%) which are madeby Nippon Kokuen L.T.D.

Examples of commercially available artificial graphites usable in thepresent invention are "RA-3000", "RA-15", "RA-44", "GX-600" and "G-6S"which are made by Chuetsu Graphite Works Co., Ltd.; "HAG-15", "PAG-15","SGS-25", "SGS-15", "SGS-5", "SGS-1", "SGP-25", "SGP-15", "SGP-5","SGP-1", "SGO-25", "SGO-15", "SGO-5", "SGO-1", "SGX-25", "SGX-15","SGX-5" and "SGX-1" made by Nippon Kokuen L.T.D., as well as high-puritygraphite having a purity of at least 99.9% from the same manufacturer,including "QP-2", "QP-5", "QP-10" and "QP-20".

Examples of commercially available artificial graphites produced byfurther processing or modifying graphite are "APO-Pi5", "AOP-B5","AOP-A5" and "AOP-T1" which are made by Nippon Kokuen L.T.D. and haveincreased dispersibility into resins by surface-treating naturalgraphite powder with pitch, an acrylic resin or a titanate.

Kish as described before and available from The Kansai Coke andChemicals Co., Ltd., which does not fall into the category of the abovenatural and artificial graphites, is also usable as the carbon materialof the present invention.

The carbon material used in the present invention may consist only ofone of the above graphites or, may comprise it as a principal componentwhile incorporating other carbon materials.

The electrolyte solution used in the present invention utilizes asolvent comprising a specific organic compound, that is, at least onecyclic compound selected from the group consisting of ethylene carbonate(EC), ethylene thiocarbonate, γ-thiobutyrolactone, α-pyrrolidone,γ-butyrolactone (γ-BL), propylene carbonate, 1,2-butylene carbonate,2,3-butylene carbonate, γ-valerolactone, γ-ethyl-γ-butyrolactone,β-methyl-γ-butyrolactone, thiolane, pyrazolidine, pyrrolidine,tetrahydrofuran, 3-methyltetra-hydrofuran, sulfolane, 3-methylsulfolane,2-methylsulfolane, 3-ethylsulfolane and 2-ethylsulfolane.

Preferred among the above cyclic compounds are those having noreadily-decomposable groups, i.e. ethylene carbonate, ethylenethiocarbonate, γ-thiobutyrolactone, α-pyrrolidone, γ-butyrolactone,thiolane, pyrazolidine, pyrrolidine, tetrahydrofuran and sulfolane.These preferred cyclic compounds are stable and do not generate gasesunder the oxidation-reduction atmosphere during charge and discharge ofthe battery and in this point differ from other cyclic compounds havingreadily decomposable methyl groups or the like, which are readilyabsorbed on active points of graphite, such as propylene carbonate,1,2-butylene carbonate, 2,3-butylene carbonate, γ-valerolactone,γ-ethyl-γ-butyrolactone and β-methyl-γ-butyrolactone. Thus, with thepreferred cyclic compounds insertion of lithium into graphite is nothindered during charge and there does not occur polarization due to gasoverpotential during charge or discharge.

The electrolyte solution in the present invention may comprise only oneof the above solvents or, as required, two or more.

Examples of preferred solvents are, those consisting of single solvent,such as ethylene carbonate, γ-butyrolactone and sulfolane, mixedsolvents comprising ethylene carbonate and γ-butyrolactone and mixedsolvents comprising ethylene carbonate, γ-butyrolactone and sulfolane,among which more preferred for the purpose of providing a large batterycapacity and high initial charge-discharge efficiency are ethylenecarbonate, γ-butyrolactone and sulfolane. Particularly preferred isethylene carbonate.

Where a mixed solvent of ethylene carbonate with γ-butyrolactone orsulfolane is used, the use of a mixed solvent containing 20% to 80% byvolume of ethylene carbonate results in remarkably large batterycapacity in high-rate discharge.

Ethylene carbonate (m.p.: 39° to 40° C.) or sulfolane (m.p.: 28.9° C.),which is solid at room temperature, may be used after being dissolved inan ether-based low-boiling point solvent, such as 1,2-dimethoxyethane(DME), 1,2-diethoxy-ethane (DEE) or ethoxymethoxyethane (EME) or anester-based low-boiling point solvent such as dimethyl carbonate (DMC)or diethyl carbonate (DEC). Even γ-butyrolactone, which is liquid atroom temperature, is preferably used in the form of a mixed solventcomprising one of the above low-boiling point solvents, for the purposeof permitting the resulting battery to develop excellent low-temperaturecharacteristics.

Among the mixed solvents used in the present invention and comprising acyclic compound and a low-boiling point solvent, those comprising acyclic carbonate and dimethyl carbonate are excellent in, particularly,high-rate discharge characteristics thanks to high conductivity ofdimethyl carbonate, while those comprising a cyclic carbonate anddiethyl carbonate are particularly excellent in low-temperaturedischarge characteristic thanks to the low viscosity and high ionconductivity at low temperatures of diethyl carbonate.

The term "low-boiling point solvents" herein means those having aboiling point of not more than 150° C.

Where mixed solvents comprising one of the above low-boiling pointsolvents and ethylene carbonate is used, the use of a mixed solventcontaining 20% to 80% by volume of ethylene carbonate results inremarkably large battery capacity in high-rate discharge. When a mixedsolvent containing at least 20% by volume of ethylene carbonate is usedas an electrolyte solvent, the lithium secondary battery of the presentinvention will have a remarkably large discharge capacity.

The electrolyte solution in the present invention is prepared bydissolving, in the above-described solvent, an electrolyte solute suchas LiPF₆, LiBF₄, LiClO₄, LiCF₃ SO₃, LiC₄ F₉ SO₃, LiN(CF₃ SO₂)₂ orLiAsF₆.

These solutes are dissolved in the solvent to a concentration ofpreferably 0.1 to 3 moles/liter, more preferably 0.5 to 1.5 moles/liter.

FIG. 1 is a graph showing the charge-discharge cycle characteristics ofthe battery of the present invention comprising graphite (Lc: 2000 Å;d₀₀₂ : 3.354 Å; Average Particle Diameter: 12 μm; Specific Surface Area:7.5 m² /g; True Density: 2.25 g/cm³) as a negative electrode materialand a comparison battery comprising coke (Lc: 45 Å; d₀₀₂ : 3.462 Å;Average Particle Diameter: 14 μm; Specific Surface Area: 4.2 m² /g; TrueDensity: 2.04 g/cm³) as a negative electrode. The ordinate of the graphrepresents the potential of the negative electrode against Li/Li⁺ singleelectrode potential, and the abscissa represents the capacity (mAh/g)per gram of the carbon material (graphite or coke). In the FIGURE, thesolid line shows the charge-discharge cycle characteristics of thebattery of the present invention and the broken line that of thecomparison battery, while the arrow marks indicate the direction of thenegative electrode potential increasing or decreasing, during dischargeor charge. The charge-discharge characteristics of the FIGURE wereobtained with the batteries both utilizing an electrolyte solvent of a1/1 by volume mixed solvent of ethylene carbonate and dimethyl carbonatecontaining 1M (mole/liter) LiPF₆.

The charge-discharge characteristic of the comparison battery are firstexplained with reference to FIG. 1. The negative electrode potential,which is about 3 (V) before initial charge (point a), gets closer to theLi/Li+ single electrode potential (this is the base, i.e. 0 V, for thenegative electrode potential values of the ordinate), as the initialcharge proceeds and Li is occluded in coke, and finally reaches thepoint b (negative electrode potential: 0 V, capacity: about 300 mAh/g).The color of coke turns light brown or red at this point. The firstdischarge is then conducted. The negative electrode potential increaseswith the proceeding of the discharge and finally reaches the point c(capacity: 50 to 100 mAh/g) that shows discharge termination potential(about 1 V). In the course of the first discharge the negative electrodepotential does not retrace the route followed during the initial chargebut reaches the point c, thus presenting hysteresis. This is due to thefact that an amount of Li corresponding to P in the FIGURE has beencaught by the coke and that, in the electrode reaction during thesucceeding charge-discharge cycles, only the remaining Li in an amountof Q can participate in the reaction. The negative electrode potentialchanges, when charge-discharge cycle is repeated thereafter, in cyclesas c→b→c→b . . . .

The charge-discharge cycle of the battery of the present invention isnext explained. In the same manner as with the comparison battery, thenegative electrode potential, which is about 3 (V) before initial charge(point a), gets closer to the Li/Li⁺ single electrode potential, as theinitial charge proceeds and Li is occluded in graphite, and finallyreaches the point d where the potential against the single electrodepotential is 0 V (capacity: 375 mAh/g). The color of graphite turns goldat the point d, which, as well as X-ray diffraction, indicates that C₆Li has been formed. The first discharge is then conducted. The negativeelectrode potential increases with the proceeding of the discharge andfinally reaches the point e (capacity: 25 mAh/g) that shows dischargetermination potential (about 1 V). The negative electrode potentialchanges, when charge-discharge cycle is repeated thereafter, in cyclesas e→d→e→d . . . .

The battery characteristics of the battery of the present invention andthat of comparison are compared based on the charge-dischargecharacteristics shown in FIG. 1. The battery of the present inventionhas a large initial charge capacity per gram of graphite of about 375mAh/g (point d) at the initial charge, while the comparison battery hasa small charge capacity per gram of coke of about 300 mAh/g (point b).Furthermore, with the battery of the present invention the capacity pergram of graphite up to the discharge termination potential, 1 V, is aslarge as about 350 mAh/g (d-e), while that per gram of coke with thecomparison battery is as small as 200 to 250 mAh/g (b-c).

This fact means that the battery of the present invention has highercharge-discharge efficiency than that of the comparison battery.

It is also noted that: while the charge-discharge curve of the batteryof the present invention is almost flat during discharge of from thepoint d to e and shows a rapid increase of negative electrode potentialwhen the discharge process comes close to the point e, thecharge-discharge curve of the comparison battery gradually increaseswhen proceeding from the point b to c.

This fact means that the battery of the present invention is superior tothe comparison battery in the flatness of discharge voltage.

That the battery of the present invention has higher charge-dischargeefficiency and flatter discharge voltage than those of the comparisonbattery further means that the battery of the present invention haslarger discharge capacity than the comparison battery.

Other features of the invention will become apparent in the course ofthe following description of exemplary embodiments which are given forillustration of the invention and are not intended to be limitingthereof.

EXAMPLES Example 1

(Example 1-1˜1-3)

(Preparation of positive electrode)

Cobalt carbonate and lithium carbonate were mixed in a atom ratio ofCo:Li of 1:1, and the mixture was heat treated at 900° C. in the air for20 hours to give LiCoO₂.

The LiCoO₂ thus obtained as a positive electrode material was mixed witha conductor of acetylene black and a binder of fluororesin dispersion0.1 g/cc of polytetrafloroethylene (PTFE) dispersed in water! in a ratioby weight of 90:6:4 to give a material for preparing a positiveelectrode. The material was rolled onto an aluminum foil (thickness: 20μm) that served as a current collector and heat treated under vacuum ata temperature of 250° C. for 2 hours, to give a positive electrode.

(Preparation of negative electrode)

Materials for preparing a negative electrode were obtained by mixingeach of China natural graphite (Lc>1000 Å; d₀₀₂ =3.354 Å; AverageParticle Diameter: 12 μm; Specific Surface Area: 7.5 m² /g; TrueDensity: 2.25 g/cm³), artificial graphite (Lc=350 Å; d₀₀₂ =3.364 Å;Average Particle Diameter: 10 μm; Specific Surface Area: 10 m² /g; TrueDensity: 2.25 g/cm³), and Lonza graphite (Lc=260 Å; d₀₀₂ =3.363 Å;Average Particle Diameter: 15 μm; Specific Surface Area: 14.0 m² /g;True Density: 2.25 g/cm³), all with a particle diameter of 2 μm to 14 μm(average particle diameter: 12 μm), with a binder of fluororesindispersion 0.1 g/cc of PTFE dispersed in water! in a ratio by weight of95:5. These materials were each rolled on a current collector of analuminum foil (thickness: 20 μm) and heat treated under vacuum at 250°C. for 2 hours, to give negative electrodes each containing one of theabove carbon materials. When a graphite having an average particlediameter of 1 to 30 μm is used for the negative electrode, the lithiumsecondary battery of the present invention will have a large dischargecapacity and high initial charge-discharge efficiency.

(Preparation of electrolyte solution)

An electrolyte solution was prepared by dissolving LiPF6 in a 1/1 byvolume mixed solvent of ethylene carbonate and dimethyl carbonate to aconcentration of 1 mole/liter. The use of ethylene carbonate in anamount of 20% to 80% by volume based on the volume of the solventresults in remarkably large discharge capacity.

(Preparation of batteries BA 1 through 3)

Cylindrical nonaqueous electrolyte solution secondary batteries (batterysize: 14.2 mm diameter, 50.0 mm height) were prepared from the abovepositive electrode, negative electrode and electrolyte. BA1, BA2 and BA3denote those utilizing, as a carbon material, natural graphite (Example1-1), artificial graphite (Example 1-2) and Lonza graphite (Example1-3), respectively. An ion-permeable polypropylene sheet (CELGARD, madeby Daicel Co.) was used as a separator.

FIG. 2 is a sectional view of the thus prepared battery BA1 (or 2, or3), which comprises a positive electrode 1, negative electrode 2, aseparator 3 interposed between and separating these two electrodes, apositive electrode lead 4, a negative electrode lead 5, a positiveelectrode external terminal 6, a negative electrode can 7 and otherparts. The positive electrode 1 and the negative electrode 2 are housedin the negative electrode can 7, while being spirally wound up with theseparator 3 inter-posed between them, the separator containing anelectrolyte solution injected thereinto. The positive electrode 1 isconnected via the positive electrode lead 4 to the positive electrodeexternal terminal 6 and the negative electrode 2 is connected via thenegative electrode lead 5 to the negative electrode can 7. The batteryis thus capable of permitting the chemical energy generated inside it tobe taken out as electrical energy.

Comparison Example 1

Example 1-1 was repeated except for using coke (Lc=45 Å; d₀₀₂ =3.462 Å;Average Particle Diameter: 14 μm; Specific Surface Area: 4.2 m² /g; TrueDensity: 2.04 g/cm³) as a negative electrode material, to prepare acomparison battery BC1.

Charge-discharge characteristics of the batteries

FIG. 3 is a graph showing the charge-discharge characteristics at 250 mA(constant-current discharge) from the second cycle on of the batteriesBA1 through BA3 of the present invention and the comparison battery BC1,where the ordinate represents the voltage (V) and the abscissarepresents the time (h). FIGS. 4 and 5 each show the charge-dischargecharacteristics of the battery BA1 or BA2 as compared with that of thecomparison battery BC1, where the ordinate represents the negativeelectrode potential (V) against Li/Li+ single electrode potential andthe abscissa represents the charge-discharge capacity (mAh/g). It isunderstood from these FIGURES that the batteries BA1 through BA3 of thepresent invention are superior to the comparison battery BC1 incharge-discharge characteristics. FIG. 6 is a graph showing the cyclecharacteristics of the batteries BA1 and BA2 of the present inventionand the comparison battery BC1, with the ordinate representing thedischarge capacity (mAh/g) and the abscissa the cycle number. As seenfrom the FIGURE, the batteries BA1 and BA2 of the present inventiondevelop better cycle characteristics than the comparison battery BC1.These batteries were also, after being charged, kept at a roomtemperature for 1 month and tested for storage capability. Then, theself-discharge rate was 2 to 5%/month for the batteries BA1 through BA3of the present invention and 15%/month for the comparison battery BC1.

Example 2

Example 1-1 was repeated except for using, instead of the China naturalgraphite, a mixture of 100 parts by weight of the natural graphite and 5parts by weight of carbon black having an Lc of 8 Å, to obtain abattery; BA5, according to the present invention.

FIG. 7 is a graph showing the cycle characteristics of the thus preparedbattery BA5, where the ordinate represents the discharge capacity of thebattery (mAh/g) and the abscissa the cycle number. FIG. 7 also shows forcomparison purposes the cycle characteristics of the battery BA1utilizing as a carbon material graphite only and the battery BC1utilizing coke.

As seen from the FIGURE, the battery BA5 develops, thanks to littledropping off of the carbon material from the electrode, better cyclecharacteristics than that utilizing graphite only, to say nothing ofthat utilizing coke.

Example 3

Example 1-1 was repeated except for using, instead of the 1/1 by volumemixed solvent of ethylene carbonate (EC) and dimethyl carbonate (DMC) asan electrolyte solvent, a 1/1 by volume mixed solvent of ethylenecarbonate and diethyl carbonate (DEC) , a 1/1 by volume mixed solvent ofethylene carbonate and dipropyl carbonate (DPC) and 1,3-dioxolane(1,3-DOL), respectively, to prepare a battery BA6 according to thepresent invention, a comparison battery BC2 and a conventional battery.

FIG. 8 is a graph showing the charge-discharge characteristics of thesebatteries, with the ordinate representing the negative electrodepotential (V) and the abscissa representing the charge-dischargecapacity.

As seen from the FIGURE, the battery BA6 develops, like that of BA1,better charge-discharge characteristics than the comparison battery BC2and the conventional battery.

Example 4

Negative electrodes were prepared from 13 types of carbon materialshaving different d-values (d₀₀₂) of the lattice plane (002) obtained bythe X-ray diffraction method thereof. The properties of the carbonmaterials are shown in Table 2. The X-ray diffraction method wasconducted under the following measuring conditions (hereinafter the samewill apply).

Radiation source: CuK α

Slit conditions: divergence slit 1°, scattering slit 1° and receivingslit 0.3 mm.

Gonioradius: 180 mm

Graphite curved crystalline monochromator.

Using the 13 negative electrodes thus prepared 13 batteries wereobtained in the same manner as in Example 1.

FIG. 9 is a graph showing the relationship between the d₀₀₂ value of acarbon material and the discharge capacity of the battery utilizing it,with the ordinate representing the discharge capacity (mAh/g) of thebattery and the abscissa the d₀₀₂ value of the carbon material used.

As seen from the FIGURE, batteries utilizing a graphite having a d₀₀₂ of3.354 to 3.370 have large discharge capacities.

                                      TABLE 2    __________________________________________________________________________             K1   K2   K3  K4  K5  K6  K7  K8  K9  K10 K11 K12 K13    __________________________________________________________________________    d.sub.002 (Å)             3.354                  3.368                       3.378                           3.385                               3.401                                   3.440                                       3.469                                           3.495                                               3.556                                                   3.630                                                       3.710                                                           3.742                                                               3.781    Lc (Å)             2000 2000 810 620 43  30  25  11  9   12  15  17  8    True Density             2.25 2.25 2.13                           2.10                               1.98                                   1.92                                       1.86                                           1.72                                               1.61                                                   1.45                                                       1.31                                                           1.13                                                               1.02    (g/cm.sup.3)    Specific Surface             7.5  6.3  6.9 7.0 6.9 7.2 8.9 9.3 7.1 6.8 7.5 8.1 6.9    Area (m.sup.2 /g)    Average Particle             12   14   12  12  12  10  15  12  14  16  11  12  12    Diameter (μm)    __________________________________________________________________________

Example 5

Negative electrodes were prepared from 12 types of carbon materialshaving different true densities. The properties of the carbon materialsare shown in Table 3. Using the 12 negative electrodes thus prepared 12batteries were obtained in the same manner as in Example 1.

FIG. 10 is a graph showing the relationship between the true density ofa carbon material and the discharge capacity of the battery utilizingit, with the ordinate representing the discharge capacity (mAh/g) of thebattery and the abscissa the true density (g/cm³) of the carbon materialused.

As seen from the FIGURE, batteries utilizing a graphite having a truedensity of 1.9 to 2.25 g/cm³ have large discharge capacities.

                                      TABLE 3    __________________________________________________________________________              M2  M3  M4   M5  M6   M7       M8  M9   M10 M11  M12    __________________________________________________________________________    d.sub.002 (Å)              3.3514                  3.354                      3.354                           3.370                               3.363                                    3.377                                        3.359                                             3.363                                                 3.398                                                      3.440                                                          3.490                                                               3.601    Lc (Å)              790 440 2000 410 220  205 190  175 8.5  18  12   11    True Density (g/cm.sup.3)              2.30                  2.29                      2.25 2.15                               2.00 1.91                                        1.87 1.80                                                 1.68 1.52                                                          1.30 1.03    Specific Surface              6.9 7.2 7.5  7.0 6.1  7.1 7.0  6.0 7.0  7.8 9.9  12    Area (m.sup.2 /g)    Average Particle              12  12  12   12  16   12  10   16  12   14  12   14    Diameter (μm)    __________________________________________________________________________

Example 6

Negative electrodes were prepared from 9 types of carbon materialshaving different average particle diameter. The properties of the carbonmaterials are shown in Table 4. Using the 9 negative electrodes thusprepared 9 batteries were obtained in the same manner as in Example 1.

FIG. 11 is a graph showing the relationship between the average particlediameter (wherein the cumulative volume is 50% in particle sizedistribution) of a carbon material and the discharge capacity of thebattery utilizing it, with the ordinate representing the dischargecapacity (mAh/g) of the battery and the abscissa the average particlediameter (μm) of the carbon material used.

As seen from the FIGURE, batteries utilizing a graphite having anaverage particle diameter of 1 to 30 μm have large discharge capacities.

                                      TABLE 4    __________________________________________________________________________              N1   N2   N3   N4   N5   N6   N7   N8   N9    __________________________________________________________________________    d.sub.002 (Å)              3.354                   3.354                        3.354                             3.354                                  3.354                                       3.354                                            3.354                                                 3.354                                                      3.354    Lc (Å)              2000 2000 2000 2000 2000 2000 2000 2000 2000    True Density (g/cm.sup.3)              2.23 2.23 2.23 2.23 2.23 2.23 2.23 2.23 2.23    Specific Surface              75   30   18   15   8.5  2.0  1.0  0.3  0.2    Area (m.sup.2 /g)    Average Particle              0.25 0.5  1    3    10   20   30   40   50    Diameter (μm)    __________________________________________________________________________

Example 7

Negative electrodes were prepared from 13 types of carbon materialshaving different specific surface areas. The properties of the carbonmaterials are shown in Table 5. Using the 13 negative electrodes thusprepared 13 batteries were obtained in the same manner as in Example 1.

FIG. 12 is a graph showing the relationship between the specific surfacearea (obtained a BET method employing N₂ gas) of a carbon material andthe discharge capacity of the battery utilizing it, with the ordinaterepresenting the discharge capacity (mAh/g) of the battery and theabscissa the specific surface area (m² /g) of the carbon material used.

As seen from the FIGURE, batteries utilizing a graphite having aspecific surface area of 0.5 to 50 m² /g have large dischargecapacities.

                                      TABLE 5    __________________________________________________________________________              P1   P2   P3   P4   P5   P6   P7    __________________________________________________________________________    d.sub.002 (Å)              3.354                   3.354                        3.354                             3.354                                  3.354                                       3.354                                            3.354    Lc (Å)              2000 2000 2000 2000 2000 2000 2000    True Density (g/cm.sup.3)              2.23 2.23 2.23 2.23 2.23 2.23 2.23    Specific Surface              0.1  0.4  0.6  1.0  2.0  3.3  6.2    Area (m.sup.2 /g)    Average Particle              80   38   35   30   20   16   14    Diameter (μm)    __________________________________________________________________________                   P8   P9   P10  P11  P12  P13    __________________________________________________________________________    d.sub.002 (Å)                   3.354                        3.354                             3.354                                  3.354                                       3.354                                            3.354    Lc (Å)     2000 2000 2000 2000 2000 2000    True Density (g/cm.sup.3)                   2.23 2.23 2.23 2.23 2.23 2.23    Specific Surface                   12   20   40   60   100  1000    Area (m.sup.2 /g)    Average Particle                   5    0.6  0.4  0.3  0.15 0.05    Diameter (μm)    __________________________________________________________________________

Example 8

Negative electrodes were prepared from 11 types of carbon materialshaving different Lc's. The properties of the carbon materials are shownin Table 6. Using the 11 negative electrodes thus prepared 11 batterieswere obtained in the same manner as in Example 1.

FIG. 13 is a graph showing the relationship between the Lc of a carbonmaterial and the discharge capacity of the battery utilizing it, withthe ordinate representing the discharge capacity (mAh/g) of the batteryand the abscissa the Lc (Å) of the carbon material used.

As seen from the FIGURE, batteries utilizing a graphite having an Lc ofat least 200 Å have large discharge capacities.

                                      TABLE 6    __________________________________________________________________________              Q1 Q2 Q3 Q4  Q5  Q6  Q7  Q8  Q9   Q10  Q11    __________________________________________________________________________    d.sub.002 (Å)              3.49                 3.46                    3.47                       3.47                           3.48                               3.376                                   3.377                                       3.367                                           3.359                                                3.359                                                     3.354    Lc (Å)              10 30 70 100 115 120 150 210 1000 1500 2000    True Density (g/cm.sup.3)              1.90                 1.89                    1.89                       1.97                           1.99                               1.70                                   1.80                                       2.03                                           2.24 2.25 2.25    Specific Surface              6.5                 7.2                    8.1                       6.3 7.2 6.9 7.0 6.3 6.7  7.0  7.5    Area (m.sup.2 /g)    Average Particle              16 14 18 11  12  12  12  14  11   9    12    Diameter (μm)    __________________________________________________________________________

Example 9

Example 1-1 was repeated except for using 1 mole/liter electrolytesolutions of LiPF₆ in solvents as shown in Table 7, to prepare 21 typesof batteries according to the present invention. The batteries thusprepared were discharged at 100 mA and tested for their graphitecharacteristics capacity per unit weight (mAh/g) and initialcharge-discharge efficiency (%)!, battery characteristics batterycapacity (mAh), self-discharge rate (%/month), cycle life (times) andcharge-discharge efficiency (%)!. The results are shown in Table 7.

Comparative Example 2

Example 1-1 was repeated except for using an electrolyte solution of a 1mole/liter LiPF₆ solution in 1,3-dioxolane, to prepare a conventionalbattery. The battery thus prepared was discharged at 100 mA and thentested for the same items as those in Example 9. The results are alsoshown in Table 7.

                                      TABLE 7    __________________________________________________________________________                 Graphite characteristics                               Battery characteristics    (+) LiCoO.sub.2 /(-) graphite                 Capacity per                       Initial charge-dis-                                    Self-dis-                                          Cycle                                              Charge-discharge    Single solvent shown below                 unit weight                       charge efficiency                               Capacity                                    charge rate                                          life                                              efficieny    __________________________________________________________________________    Ethylene carbonate                 350   95      600  5     >1,000                                              100    Propylene carbonate                 230   60      420  25    >500                                              97    1,2-Butylene carbonate                 270   65      360  20    >300                                              95    2,3-Butylene carbonate                 200   60      400  25    >300                                              95    Ethylene thiocarbonate                 190   80      350  10    >300                                              95    γ-Thiobutyrolactone                 200   85      400  10    >300                                              95    α-pyrrolidone                 180   75      380  10    >300                                              95    γ-butyrolactone                 320   95      500  5     >1,000                                              100    γ-valerolactone                 230   90      360  10    >500                                              97    γ-ethyl-γ-butyrolactone                 190   85      380  10    >500                                              97    β-methyl-γ-butyrolactone                 170   80      380  10    >300                                              95    Thiolane     200   80      400  15    >300                                              95    Pyrazolidine 190   80      380  15    >500                                              97    Pyrrolidine  180   85      380  10    >300                                              95    Tetrahydrofuran                 230   90      420  10    >500                                              97    3-Methyltetrahydrofuran                 220   80      420  15    >300                                              95    Sulfolane    300   95      480  5     >1,000                                              100    3-Methylsulfolane                 280   85      450  10    >500                                              97    2-Methylsulfolane                 260   80      450  10    >500                                              97    3-Ethylsulfolane                 250   85      440  15    >300                                              95    2-Ethylsulfolane                 250   85      440  15    >300                                              95    1,3-dioxolane                 100   60      150  50    <50 70    __________________________________________________________________________

Example 10

Example 1-1 was repeated except for using electrolyte solutions of a 1mole/liter LiPF₆ solution in each of the mixed solvents as shown inTable 8, to prepare 21 types of batteries according to the presentinvention. The batteries thus prepared were discharged at 100 mA andthen tested for the same items as those in Example 9. The results arealso shown in Table 8.

                                      TABLE 8    __________________________________________________________________________    (+) LiCoO.sub.2 /(-) graphite                 Graphite characteristics                               Battery characteristics    Dimethyl carbonate:solvent                 Capacity per                       Initial charge-dis-                                    Self-dis-                                          Cycle                                              Charge-discharge    shown below = 1:1                 unit weight                       charge efficiency                               Capacity                                    charge rate                                          life                                              efficieny    __________________________________________________________________________    Ethylene carbonate                 355   95      610  5     >1,000                                              100    Propylene carbonate                 235   60      425  25    >500                                              97    1,2-Butylene carbonate                 270   65      360  20    >300                                              95    2,3-Butylene carbonate                 200   60      400  25    >300                                              95    Ethylene thiocarbonate                 190   80      350  10    >300                                              95    γ-Thiobutyrolactone                 200   85      400  25    >300                                              95    α-pyrrolidone                 185   75      385  10    >300                                              95    γ-butyrolactone                 310   95      520  5     >1,000                                              100    γ-valerolactone                 235   90      370  10    >500                                              97    γ-ethyl-γ-butyrolactone                 195   85      385  10    >300                                              97    β-methyl-γ-butyrolactone                 175   80      385  10    >300                                              95    Thiolane     205   80      410  15    >300                                              95    Pyrazolidine 195   80      380  15    >500                                              97    Pyrrolidine  185   85      380  10    >300                                              95    Tetrahydrofuran                 235   90      425  10    >500                                              97    3-Methyltetrahydrofuran                 230   80      420  15    >300                                              95    Sulfolane    305   95      485  5     >1,000                                              100    3-Methylsulfolane                 285   85      460  10    >500                                              97    2-Methylsulfolane                 265   80      450  10    >500                                              97    3-Ethylsulfolane                 250   85      440  15    >300                                              95    2-Ethylsulfolane                 250   85      440  15    >300                                              95    __________________________________________________________________________

Example 11

Example 1-1 was repeated except for using electrolyte solutions of a 1mole/liter LiPF₆ solution in each of the mixed solvents as shown inTable 9, to prepare 21 types of batteries according to the presentinvention. The batteries thus prepared were discharged at 100 mA andthen tested for the same items as those in Example 9. The results arealso shown in Table 9.

                                      TABLE 9    __________________________________________________________________________    (+) LiCoO.sub.2 /(-) graphite                 Graphite characteristics                               Battery characteristics    Dimethyl carbonate:solvent                 Capacity per                       Initial charge-dis-                                    Self-dis-                                          Cycle                                              Charge-discharge    shown below = 1:1                 unit weight                       charge efficiency                               Capacity                                    charge rate                                          life                                              efficieny    __________________________________________________________________________    Ethylene carbonate                 350   95      600  5     >1,000                                              100    Propylene carbonate                 230   60      420  25    >500                                              97    1,2-Butylene carbonate                 260   65      350  20    >300                                              95    2,3-Butylene carbonate                 200   60      400  25    >300                                              95    Ethylene thiocarbonate                 185   80      345  10    >300                                              95    γ-Thiobutyrolactone                 195   85      395  10    >300                                              95    α-pyrrolidone                 180   75      380  10    >300                                              95    γ-butyrolactone                 300   95      500  5     >1,000                                              100    γ-valerolactone                 230   90      360  10    >500                                              97    γ-ethyl-γ-butyrolactone                 190   85      380  10    >500                                              97    β-methyl-γ-butyrolactone                 170   80      370  10    >300                                              95    Thiolane     200   80      400  15    >300                                              95    Pyrazolidine 190   80      380  15    >500                                              97    Pyrrolidine  180   85      380  10    >300                                              95    Tetrahydrofuran                 230   90      420  10    >500                                              97    3-Methyltetrahydrofuran                 225   80      420  15    >300                                              95    Sulfolane    300   95      475  5     >1,000                                              100    3-Methylsulfolane                 280   85      455  10    >500                                              97    2-Methylsulfolane                 260   80      450  10    >500                                              97    3-Ethylsulfolane                 250   85      445  15    >300                                              95    2-Ethylsulfolane                 250   85      440  15    >300                                              95    __________________________________________________________________________

Example 12

Example 1-1 was repeated except for using electrolyte solutions of a 1mole/liter LiPF₆ solution in each of the mixed solvents as shown inTable 10, to prepare 21 types of batteries according to the presentinvention. The batteries thus prepared were discharged at 100 mA andthen tested for the same items as those in Example 9. The results arealso shown in Table 10.

                                      TABLE 10    __________________________________________________________________________    (+) LiCoO.sub.2 /(-) graphite                 Graphite characteristics                               Battery characteristics    1,2-Dimethoxyethane:solvent                 Capacity per                       Initial charge-dis-                                    Self-dis-                                          Cycle                                              Charge-discharge    shown below = 1:1                 unit weight                       charge efficiency                               Capacity                                    charge rate                                          life                                              efficieny    __________________________________________________________________________    Ethylene carbonate                 360   95      620  10    >300                                              95    Propylene carbonate                 240   60      440  50    >50 70    1,2-Butylene carbonate                 280   65      380  40    >100                                              80    2,3-Butylene carbonate                 210   60      420  50    >50 70    Ethylene thiocarbonate                 200   80      370  20    >200                                              90    γ-Thiobutyrolactone                 210   85      420  20    >200                                              90    α-pyrrolidone                 190   75      400  20    >200                                              90    γ-butyrolactone                 330   95      520  10    >300                                              95    γ-valerolactone                 240   90      380  20    >200                                              90    γ-ethyl-γ-butyrolactone                 200   85      400  20    >200                                              90    β-methyl-γ-butyrolactone                 180   80      400  20    >200                                              90    Thiolane     210   80      420  30    >150                                              85    Pyrazolidine 200   80      400  30    >150                                              85    Pyrrolidine  190   85      400  20    >200                                              90    Tetrahydrofuran                 240   90      440  20    >200                                              90    3-Methyltetrahydrofuran                 230   80      440  30    >150                                              85    Sulfolane    310   95      500  10    >300                                              95    3-Methylsulfolane                 290   85      470  20    >200                                              90    2-Methylsulfolane                 270   80      470  20    >200                                              90    3-Ethylsulfolane                 260   85      460  30    >150                                              85    2-Ethylsulfolane                 260   85      460  30    >150                                              85    __________________________________________________________________________

Example 13

Example 9 was repeated except for using LiNiO₂ instead of LiCoO₂ as apositive electrode material, to prepare 21 types of batteries accordingto the present invention. The batteries thus prepared were discharged at100 mA and then tested for the same items as those in Example 9. Theresults are also shown in Table 11.

                                      TABLE 11    __________________________________________________________________________    (+) LiNiO.sub.2 /(-) graphite                 Graphite characteristics                               Battery characteristics    Single solvent shown below                 Capacity per                       Initial charge-dis-                                    Self-dis-                                          Cycle                                              Charge-discharge    shown below = 1:1                 unit weight                       charge efficiency                               Capacity                                    charge rate                                          life                                              efficieny    __________________________________________________________________________    Ethylene carbonate                 350   95      550  5     >1,000                                              100    Propylene carbonate                 230   60      370  25    >500                                              97    1,2-Butylene carbonate                 270   65      310  20    >300                                              95    2,3-Butylene carbonate                 200   60      350  25    >300                                              95    Ethylene thiocarbonate                 190   80      300  10    >300                                              95    γ-Thiobutyrolactone                 200   85      350  10    >300                                              95    α-pyrrolidone                 180   75      330  10    >300                                              95    γ-butyrolactone                 320   95      450  5     >1,000                                              100    γ-valerolactone                 230   90      310  10    >500                                              97    γ-ethyl-γ-butyrolactone                 190   85      330  10    >500                                              97    β-methyl-γ-butyrolactone                 170   80      330  10    >300                                              95    Thiolane     200   80      350  15    >300                                              95    Pyrazolidine 190   80      330  15    >500                                              97    Pyrrolidine  180   85      330  10    >300                                              95    Tetrahydrofuran                 230   90      370  10    >500                                              97    3-Methyltetrahydrofuran                 220   80      370  15    >300                                              95    Sulfolane    300   95      430  5     >1,000                                              100    3-Methylsulfolane                 280   85      400  10    >500                                              97    2-Methylsulfolane                 260   80      400  10    >500                                              97    3-Ethylsulfolane                 250   85      390  15    >300                                              95    2-Ethylsulfolane                 250   85      390  15    >300                                              95    __________________________________________________________________________

Example 14

Example 9 was repeated except for using LiMn₂ O₄ instead of LiCoO₂ as apositive electrode material, to prepare 21 types of batteries accordingto the present invention. The batteries thus prepared were discharged at100 mA and then tested for the same items as those in Example 9. Theresults are also shown in Table 12.

                                      TABLE 12    __________________________________________________________________________    (+) LiMn.sub.2 O.sub.2 /(-) graphite                 Graphite characteristics                               Battery characteristics    Single solvent shown below                 Capacity per                       Initial charge-dis-                                    Self-dis-                                          Cycle                                              Charge-discharge    shown below = 1:1                 unit weight                       charge efficiency                               Capacity                                    charge rate                                          life                                              efficieny    __________________________________________________________________________    Ethylene carbonate                 350   95      580  5     >1,000                                              100    Propylene carbonate                 230   60      400  25    >500                                              97    1,2-Butylene carbonate                 270   65      340  20    >300                                              95    2,3-Butylene carbonate                 200   60      380  25    >300                                              95    Ethylene thiocarbonate                 190   80      330  10    >300                                              95    γ-Thiobutyrolactone                 200   85      380  10    >300                                              95    α-pyrrolidone                 180   75      360  10    >300                                              95    γ-butyrolactone                 320   95      480  5     >1,000                                              100    γ-valerolactone                 230   90      340  10    >500                                              97    γ-ethyl-γ-butyrolactone                 190   85      360  10    >500                                              97    β-methyl-γ-butyrolactone                 170   80      360  10    >300                                              95    Thiolane     200   80      380  15    >300                                              95    Pyrazolidine 190   80      360  15    >50Q                                              97    Pyrrolidine  180   85      360  10    >300                                              95    Tetrahydrofuran                 230   90      400  10    >500                                              97    3-Methyltetrahydrofuran                 220   80      400  15    >300                                              95    Sulfolane    300   95      460  5     >1,000                                              100    3-Methylsulfolane                 280   85      420  10    >500                                              97    2-Methylsulfolane                 260   80      430  10    >500                                              97    3-Ethylsulfolane                 250   85      425  15    >300                                              95    2-Ethylsulfolane                 250   85      425  15    >300                                              95    __________________________________________________________________________

Example 15

Example 1-1 was repeated except for using electrolyte solutions of a 1mole/liter LiPF₆ solution in each of mixed solvents as shown in Table13, to prepare 5 types of batteries according to the present invention.The batteries thus prepared were discharged at 1 A and then tested forthe same items as those in Example 9. The results are also shown inTable 13.

                                      TABLE 13    __________________________________________________________________________    (+) LiCoO.sub.2 /(-) graphite                 Graphite characteristics                               Battery characteristics    Ethylene carbonate:solvent                 Capacity per                       Initial charge-dis-                                    Self-dis-                                          Cycle                                              Charge-discharge    shown below = 1:1                 unit weight                       charge efficiency                               Capacity                                    charge rate                                          life                                              efficieny    __________________________________________________________________________    Dimethyl carbonate                 330   95      550  5     >1,000                                              100    Diethyl carbonate                 310   95      530  5     >1,000                                              100    1,2-Dimethoxyethane                 330   95      550  10    >300                                              95    1,2-Diethoxyethane                 310   95      530  10    >300                                              95    Ethoxymethdxyethane                 310   95      530  10    >300                                              95    __________________________________________________________________________

Example 16

Example 1-1 was repeated except for using electrolyte solutions of a 1mole/liter LiPF₆ solution in each of the mixed solvents as shown inTable 14, to prepare 5 types of batteries according to the presentinvention. The batteries thus prepared were discharged at 1 A and thentested for the same items as those in Example 9. The results are alsoshown in Table 14.

                                      TABLE 14    __________________________________________________________________________    (+) LiCoO.sub.2 /(-) graphite                 Graphite characteristics                               Battery characteristics    Sulfolane:solvent                 Capacity per                       Initial charge-dis-                                    Self-dis-                                          Cycle                                              Charge-discharge    shown below = 1:1                 unit weight                       charge efficiency                               Capacity                                    charge rate                                          life                                              efficieny    __________________________________________________________________________    Dimethyl carbonate                 240   95      430  5     >1,000                                              100    Diethyl carbonate                 200   95      400  5     >1,000                                              100    1,2-Dimethoxyethane                 240   95      430  10    >300                                              95    1,2-Diethoxyethane                 200   95      400  10    >300                                              95    Ethoxymethoxyethane                 200   95      400  10    >300                                              95    __________________________________________________________________________

Example 17

Example 1-1 was repeated except for using, instead of LiPF₆, each of theelectrolyte solutes as shown in Table 15, to prepare 6 types ofbatteries according to the present invention. The batteries thusprepared were discharged at 100 mA and then tested for the same items asthose in Example 9. The results are also shown in Table 15.

Tables 7 through 15 shows that the batteries of the present inventiondevelop better battery characteristics over all the items tested thanthose of the conventional battery.

                                      TABLE 15    __________________________________________________________________________    (+) LiCoO.sub.2 /(-) graphite                Graphite characteristics                             Battery characteristics    Ethylene carbonate:                      Initial charge-                                  Self-dis-                                           Charge-    dimethyl carbonate = 1:1;                Capacity per                      discharge   charge                                       Cycle                                           discharge    Solute: shown below                unit weight                      efficiency                             Capacity                                  rate life                                           efficiency    __________________________________________________________________________    LiPF.sub.6  350   95     600  5    >1,000                                           100    LiBF.sub.4  350   95     600  5    >1,000                                           100    LiClO.sub.4 350   95     660  5    >1,000                                           100    LiCF.sub.3 SO.sub.3                350   95     66o  5    >1,000                                           100    LiC.sub.4 F.sub.9 SO.sub.3                350   95     600  5    >1,000                                           100    LiN(CF.sub.3 SO.sub.2).sub.2                350   95     600  5    >1,000                                           100    LiAsF.sub.6 350   95     600  5    >1,000                                           100    __________________________________________________________________________

Example 18

Example 1-1 was repeated except for using 11 electrolyte solutions of 1mole/liter of LiPF₆ in each of mixed solvents of ethylene carbonate andγ-butyrolactone in mixing ratios by volume of 100:0, 90:10, 80:20,70:30, 60:40, 50:50, 40:60, 30:70, 20:80, 10:90 and 0:100, respectively,to prepare 11 batteries. The batteries thus prepared were discharged at100 mA and then tested for the relationship between the battery capacityand the mixing ratio by volume.

FIG. 14 is a graph with the coordinate representing the battery capacity(mAh) and the abscissa the mixing ratio by volume (% by volume). As isunderstood from the FIGURE, with discharge at 100 mA the use of asolvent containing at least 20% by volume of ethylene carbonate resultsin large battery capacity.

Example 19

Example 1-1 was repeated except for using 11 electrolyte solutions of 1mole/liter of LiPF₆ in each of mixed solvents of ethylene carbonate,γ-butyrolactone and sulfolane in various mixing ratios by volume (% byvolume) with the latter two being always mixed in the same amounts, toprepare 11 batteries. The batteries thus prepared were discharged at 100mA and then tested for the relationship between the battery capacity andthe mixing ratio by volume.

FIG. 15 is a graph with the coordinate representing the battery capacity(mAh) and the abscissa the mixing ratio by volume (% by volume). TheFIGURE shows that, with discharge at 100 mA, the use of a solventcontaining at least 20% by volume of ethylene carbonate results in largebattery capacity.

Example 20

Example 1-1 was repeated except for using mixed solvents oftetrahydrofuran and dimethyl carbonate in various mixing ratios byvolume (% by volume) and using LiNiO₂ instead of LiCoO₂ for the positiveelectrode, to prepare 11 batteries. The batteries thus prepared weredischarged at 1 A and then tested for the relationship between thebattery capacity and the mixing ratio by volume.

FIG. 16 is a graph with the coordinate representing the battery capacity(mAh) and the abscissa the mixing ratio by volume (% by volume). TheFIGURE shows that, with discharge at 1 A, the use of a mixed solventcontaining 20 to 80% by volume of tetrahydrofuran results in remarkablylarge discharge capacity.

Example 21

Example 1-1 was repeated except for using mixed solvents of sulfolaneand diethyl carbonate in various mixing ratios (% by volume) and usingLiMn₂ O₂ instead of LiCoO₂ for the positive electrode, to prepare 11batteries. The batteries thus prepared were discharged at 1 A and thentested for the relationship between the battery capacity and the mixingratio by volume.

FIG. 17 is a graph with the coordinate representing the battery capacity(mAh) and the abscissa the mixing ratio by volume (% by volume). TheFIGURE shows that, with discharge at 1 A, the use of a mixed solventcontaining 20% to 80% by volume of sulfolane based on the volume of thesolvent results in remarkably large discharge capacity.

Example 22

Example 1-1 was repeated except for using mixed solvents of ethylenecarbonate, γ-butyrolactone and dimethyl carbonate in various mixingratios by volume (% by volume) with the former two always being mixed inthe same amounts, to prepare 11 batteries. The batteries thus preparedwere discharged at 100 mA and then tested for the relationship betweenthe battery capacity and the mixing ratio by volume.

FIG. 18 is a graph with the coordinate representing the battery capacity(mAh) and the abscissa the mixing ratio by volume (% by volume). TheFIGURE shows that, with discharge at 100 mA, the use of a solventcontaining ethylene carbonate results in large battery capacity.

Example 23

Example 1-1 was repeated except for using mixed solvents of ethylenecarbonate, γ-butyrolactone and diethyl carbonate in various mixingratios by volume (% by volume based on the volume of the solvent) withthe former two always being mixed in the same amounts, to prepare 11batteries. The batteries thus prepared were discharged at 100 mA andthen tested for the relationship between the battery capacity and themixing ratio by volume.

FIG. 19 is a graph with the coordinate representing the battery capacity(mAh) and the abscissa the mixing ratio by volume (% by volume). TheFIGURE shows that, with discharge at 100 mA, the use of a solventcontaining ethylene carbonate results in large battery capacity.

Example 24

Example 1-1 was repeated except for using mixed solvents of ethylenecarbonate and dimethyl carbonate in various mixing ratios by volume (%by volume) and using LiNiO₂ instead of LiCoO₂ for the positiveelectrode, to prepare 11 batteries. The batteries thus prepared weredischarged at 1 A and then tested for the relationship between thebattery capacity and the mixing ratio by volume.

FIG. 20 is a graph with the coordinate representing the battery capacity(mAh) and the abscissa the mixing ratio by volume (% by volume). TheFIGURE shows that, with discharge at 1 A, the use of a solventcontaining 20 to 80% by volume of ethylene carbonate results inremarkably large battery capacity.

Example 25

Example 1-1 was repeated except for changing the mixing ratio by volume(% by volume) of ethylene carbonate and diethyl carbonate, to prepare 11batteries. The batteries thus prepared were discharged at 1 A and thentested for the relationship between the battery capacity and the mixingratio by volume.

FIG. 21 is a graph with the coordinate representing the battery capacity(mAh) and the abscissa the mixing ratio by volume (% by volume). TheFIGURE shows that, with discharge at 1 A, the use of a solventcontaining 20 to 80% by volume of ethylene carbonate results inremarkably large battery capacity.

Example 26

Example 1-1 was repeated except for using mixed solvents of ethylenecarbonate, dimethyl carbonate and diethyl carbonate in various mixingratios (% by volume) with the latter two always being mixed in the sameamounts and using LiMn₂ O₄ instead of LiCoO₂ for the positive electrode,to prepare 11 batteries. The batteries thus prepared were discharged at1 A and then tested for the relationship between the battery capacityand the mixing ratio by volume.

FIG. 22 is a graph with the coordinate representing the battery capacity(mAh) and the abscissa the mixing ratio by volume (% by volume). TheFIGURE shows that, with discharge at 1 A, the use of a solventcontaining 20 to 80% by volume of ethylene carbonate results inremarkably large battery capacity.

Additional Example 1

In this Example, various graphite samples to be used as a negativeelectrode and having d-values very close to each other were used, andthe relationship between the Lc and the discharge capacity per unitweight (mAh/g) or the initial charge-discharge efficiency (%) ofgraphites was studied. A lithium metal plate was used as a positiveelectrode and a electrolyte solution of 1 mole /liter LiPF₆ in a mixedsolvent by the volume mixing ratio of 4:6 of ethylene carbonate anddimethyl carbonate was used as an electrolyte solution. The initialcharge-discharge efficiency herein was calculated by a calculationformula: (discharge capacity at the first cycle)/(charge capacity at thefirst cycle)!×100. The results are shown in FIGS. 23 through 31, whichused graphites having the following properties in Tables 16 through 24.

                                      TABLE 16    __________________________________________________________________________              A1   A2   A3   A4   A5   A6   A7   A8    __________________________________________________________________________    d.sub.002 (Å)              3.354                   3.354                        3.354                             3.354                                  3.354                                       3.354                                            3.354                                                 3.354    Lc (Å)              6.7  127  85   200  230  500  1000 2000    True Density (g/cm.sup.3)              1.42 1.62 1.80 2.20 2.22 2.23 2.25 2.25    Average Particle              10   12   12   2    12   12   12   12    Diameter (μm)    Specific Surface              7.2  6.9  7.0  7.2  7.1  7.7  7.3  7.5    Area (m.sup.2 /g)    __________________________________________________________________________

                                      TABLE 17    __________________________________________________________________________              B1   B2   B3   B4   B5   B6   B7   B8    __________________________________________________________________________    d.sub.002 (Å)              3.359                   3.359                        3.359                             3.359                                  3.359                                       3.359                                            3.359                                                 3.359    Lc (Å)              7.3  110  190  210  250  1000 1500 2000    True Density (g/cm.sup.3)              1.59 1.73 1.871                             1.95 2.20 2.24 2.25 2.23    Average Particle              10   10   10   10   10   11   9    10    Diameter (μm)    Specific Surface              6.8  7.2  7.0  7.1  6.9  6.7  7.0  7.2    Area (m.sup.2 /g)    __________________________________________________________________________

                                      TABLE 18    __________________________________________________________________________              C1   C2   C3   C4   C5   C6   C7    __________________________________________________________________________    d.sub.002 (Å)              3.362                   3.362                        3.363                             3.363                                  3.362                                       3.363                                            3.361    Lc (Å)              5.0  145  175  220  980  1750 1800    True Density (g/cm.sup.3)              1.50 1.64 1.80 2.0  2.19 2.20 2.22    Average Particle              16   16   16   16   16   16   17    Diameter (μm)    Specific Surface              5.0  5.9  6.0  6.1  5.8  5.7  5.5    Area (m.sup.2 /g)    __________________________________________________________________________

                                      TABLE 19    __________________________________________________________________________              D1   D2   D3   D4   D5   D6   D7   D8    __________________________________________________________________________    d.sub.002 (Å)              3.366                   3.367                        3.366                             3.367                                  3.367                                       3.367                                            3.366                                                 3.368    Lc (Å)              8.0  35   116  188  210  750  1000 2000    True Density (g/cm.sup.3)              1.43 1.79 1.83 1.89 2.03 2.19 2.20 2.25    Average Particle              14   14   14   15   14   13   14   14    Diameter (μm)    Specific Surface              6.2  6.0  5.9  6.5  6.3  6.2  6.4  6.3    Area (m.sup.2 /g)    __________________________________________________________________________

                                      TABLE 20    __________________________________________________________________________              E1   E2   E3   E4   E5   E6   E7   E8    __________________________________________________________________________    d.sub.002 (Å)              3.370                   3.370                        3.370                             3.370                                  3.370                                       3.370                                            3.370                                                 3.370    Lc (Å)              9.5  50   130  192  215  410  790  1000    True Density (g/cm.sup.3)              1.66 1.65 1.70 1.81 1.93 2.15 2.20 2.23    Average Particle              12   12   12   12   12   12   12   12    Diameter (μm)    Specific Surface              6.8  6.9  7.0  6.9  7.1  7.0  7.2  7.0    Area (m.sup.2 /g)    __________________________________________________________________________

                                      TABLE 21    __________________________________________________________________________              F1   F2   F3   F4   F5   F6   F7   F8    __________________________________________________________________________    d.sub.002 (Å)              3.382                   3.383                        3.382                             3.382                                  3.383                                       3.382                                            3.381                                                 3.381    Lc (Å)              6.0  18   75   154  181  210  320  720    True Density (g/cm.sup.3)              1.39 1.48 1.65 1.88 1.95 1.97 2.00 2.02    Average Particle              12   12   14   12   12   14   14   12    Diameter (μm)    Specific Surface              6.9  6.8  7.0  7.1  7.2  7.0  6.9  7.0    Area (m.sup.2 /g)    __________________________________________________________________________

                                      TABLE 22    __________________________________________________________________________              G1   G2   G3   G4   G5   G6   G7   G8    __________________________________________________________________________    d.sub.002 (Å)              3.385                   3.385                        3.386                             3.385                                  3.386                                       3.387                                            3.385                                                 3.385    Lc (Å)              8.5  25   83   145  190  220  300  620    True Density (g/cm.sup.3)              1.41 1.44 1.72 1.95 2.00 2.0  2.08 2.10    Average Particle              12   12   12   12   12   12   12   12    Diameter (μm)    Specific Surface              6.8  6.9  6.8  7.3  7.2  6.9  7.0  7.2    Area (m.sup.2 /g)    __________________________________________________________________________

                                      TABLE 23    __________________________________________________________________________              H1   H2   H3   H4   H5   H6   H7   H8    __________________________________________________________________________    d.sub.002 (Å)              3.392                   3.392                        3.393                             3.392                                  3.393                                       3.392                                            3.392                                                 3.393    Lc (Å)              15   45   73   100  170  230  290  450    True Density (g/cm.sup.3)              1.65 1.72 1.83 1.85 1.90 1.95 2.01 2.05    Average Particle              12   12   12   12   12   12   12   12    Diameter (μm)    Specific Surface              6.6  6.9  6.8  6.7  6.9  7.0  7.1  6.9    Area (m.sup.2 /g)    __________________________________________________________________________

                                      TABLE 24    __________________________________________________________________________              I1   I2   I3   I4   I5   I6   I7   I8    __________________________________________________________________________    d.sub.002 (Å)              3.398                   3.397                        3.398                             3.397                                  3.397                                       3.398                                            3.399                                                 3.398    Lc (Å)              8.5  32   50   110  160  210  250  310    True Density (g/cm.sup.3)              1.68 1.75 1.79 1.83 1.89 1.91 1.92 1.99    Average Particle              12   12   12   12   12   12   12   12    Diameter (μm)    Specific Surface              7.0  6.8  6.7  6.8  6.9  6.5  7.1  6.9    Area (m.sup.2 /g)    __________________________________________________________________________

As shown in FIGS. 23 through 27, where the graphites having a d-value ofnot more than 3.370 were used as negative electrodes, the dischargecapacity and initial charge-discharge efficiency critically changed to alarge extent starting at an Lc of 200 Å. Accordingly, in the presentinvention, the critical d-value of the graphite to be used for thenegative electrode has been found to be not more than 3.370 byconducting these experiments.

The above-described critically changing phenomena were not observed withgraphites having a d-value exceeding 3.370 (see FIGS. 28 through 31).

That is, as seen from FIGS. 23 through 27, it can be understood that thegraphites having a d-value of 3.354 to 3.370 and an Lc of at least 200 Åhave a remarkably large discharge capacity and high initialcharge-discharge efficiency.

Additional Example 2

In this Example, various graphite samples to be used as a negativeelectrode and having an Lc of at least 200 Å (according to the presentinvention) and those having an Lo of less than 200 Å (comparisonsamples) were used, and the relationship between the d-value and thedischarge capacity per unit weight (mAh/g) or the initialcharge-discharge efficiency (%) of graphites was studied. The experimentconditions employed here were the same as in Additional Example 1. Theresults are shown in FIGS. 32 through 35.

The abscissa in the graphs of these FIGURES represent the d-value and,the ordinate represent the discharge capacity in FIGS. 32 and 34 and theinitial charge-discharge efficiency in FIGS. 33 and 35.

It can be understood from FIGS. 32 and 33 that, where the graphiteshaving an Lc of at least 200 Å were used as a negative electrode, thosegraphites that have a d-value of less than 3.370 sufficiently maintainat high levels the discharge capacity (see FIG. 32) and the initialcharge-discharge efficiency (see FIG. 33).

The above-described critical phenomena, i.e. marked dependency on ad-value of the discharge capacity and initial charge-dischargeefficiency, were not observed with the graphites having an Lo of lessthan 200 Å (see FIGS. 34 and 35).

Thus, it can be understood from FIGS. 32 through 35 that the graphiteshaving an Lo of at least 200 Å and a d-value of not more than 3.370 havea significantly large discharge capacity and remarkably high initialcharge-discharge efficiency.

Additional Example 3

In this Example, various graphite samples to be used as a negativeelectrode and having the same d-value (3.354) and Lc (2000 Å) were used,and the relationship between the specific surface area and the dischargecapacity per unit weight (mAh/g) or the initial charge-dischargeefficiency (%) of the graphites was studied. The experiment conditionsemployed here were the same as in Additional Example 1. The specificsurface area herein was measured by the BET method and expressed in m²/g. The results are shown in FIG. 36, which used graphites having thefollowing properties in Table 25.

                                      TABLE 25    __________________________________________________________________________            J1  J2 J3  J4 J5  J6 J7  J8 J9  J10    __________________________________________________________________________    Average Particle            80  50 40  38 35  30 20  16 14  10    Diameter (μm)    Specific Surface            0.1 0.2                   0.3 0.4                          0.6 1.0                                 2.0 3.3                                        6.2 8.5    Area (m.sup.2 /g)    __________________________________________________________________________            J11               J12                  J13                     J14                        J15                           J16                              J17                                 J18                                    J19 J20 A8    __________________________________________________________________________    Average Particle            5  3  1  0.6                        0.5                           0.4                              0.3                                 0.25                                    0.15                                        0.05                                            1.2    Diameter (μm)    Specific Surface            12 15 18 20 30 40 60 75 100 1000                                            7.5    Area (m.sup.2 /g)    __________________________________________________________________________

It can be observed from FIG. 36, that with negative electrodes using agraphite having a specific surface area of 0.5 to 50 m² /g the dischargecapacity and the initial charge-discharge efficiency of the graphitecritically change and are maintained at high levels.

It can be also understood that with negative electrodes using a graphitehaving a specific surface area of, in particular, 1.0 to 18 m² /g, stillhigher levels among the above excellent characteristics are stablymaintained.

Here, it has been found that graphites having a specific surface area ofless than 0.5 m² /g tend to be inferior, particularly, in the initialcharge-discharge efficiency and those having a specific surface areaexceeding, particularly, 50 m² /g tend to show low discharge capacity.

Thus, it can be understood that, in the present invention, amonggraphites having a d-value of 3.354 to 3.370 and an Lc of at least 200Å, selection of those having a specific surface area in a range of 0.5to 50 m² /g realizes excellent batteries that maintain the dischargecapacity and initial charge-discharge efficiency at high levels.

Additional Example 4

In this Example, various graphite samples to be used as a negativeelectrode and having the same d-value (3.354) and Lc (2000 Å) were used,and the relationship between the average particle diameter and thedischarge capacity per unit weight (mAh/g) or the initialcharge-discharge efficiency (%) of graphites was studied. The experimentconditions employed here were the same as in Additional Example 1. Theaverage particle diameter herein is expressed in μm. The results areshown in FIG. 37, which used graphites having the following propertiesin Table 26.

                                      TABLE 26    __________________________________________________________________________            J1  J2 J3  J4 J5  J6 J7  J8 J9  J10    __________________________________________________________________________    Average Particle            80  50 40  38 35  30 20  16 14  10    Diameter (μm)    Specific Surface            0.1 0.2                   0.3 0.4                          0.6 1.0                                 2.0 3.3                                        6.2 8.5    Area (m.sup.2 /g)    __________________________________________________________________________            J11               J12                  J13                     J14                        J15                           J16                              J17                                 J18                                    J19 J20 A8    __________________________________________________________________________    Average Particle            5  3  1  0.6                        0.5                           0.4                              0.3                                 0.25                                    0.15                                        0.05                                            12    Diameter (μm)    Specific Surface            12 15 18 20 30 40 60 75 100 1000                                            7.5    Area (m.sup.2 /g)    __________________________________________________________________________

It can be observed from FIG. 37, that with negative electrodes using agraphite having an average particle diameter of 1.0 to 30 μm thedischarge capacity and the initial charge-discharge efficiency of thegraphite critically markedly change and are maintained at high levels.

Here, it has been found that graphites having an average particlediameter of less than 1.0 μm tend to be inferior, particularly, in thedischarge capacity and those having an average particle diameterexceeding, particularly, 30 μm tend to be poor both in the dischargecapacity and the initial charge-discharge capacity.

Thus, it can be understood that, in the present invention, amonggraphites having a d-value of 3.354 to 3.370 and an Lc of at least 200Å, selection of those having an average particle diameter in a range of1 to 30 μm realizes excellent batteries that maintain the dischargecapacity and initial charge-discharge efficiency at high levels.

In the above Examples, the present invention has been described when itis applied to cylindrical batteries. However, the present invention canbe applied to batteries of any shape, such as square, flat or the like,and there are no restrictions with respect to the shape of the batteriesof the present invention.

Obviously, numerous modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto be understood that within the scope of the appended claims, theinvention may be practiced otherwise than as specifically describedherein.

What is claimed is:
 1. A lithium secondary battery comprising:a negativeelectrode composed mainly of a carbon material consisting essentially ofa graphite having(a) a d-value of the lattice plane (002) obtained byx-ray diffraction thereof of 3.354 to 3.370 and (b) a crystallite sizein the c-axis direction obtained by x-ray diffraction thereof of atleast 200 Å; a positive electrode composed mainly of a compound capableof occluding and discharging lithium and which is different from thegraphite of the negative electrode; a separator between said positiveelectrode and said negative electrode; and an electrolyte solution of anelectrolyte solute dissolved in a solvent, said solvent consistingessentially of 20% to 80% by volume of ethylene carbonate and 80% to 20%by volume of at least one of dimethyl carbonate and diethyl carbonate.2. The lithium secondary battery according to claim 1, wherein saidcompound capable of occluding and discharging lithium is represented bythe formula Li_(x) MO₂ or Li_(y) M₂ O₄ wherein M is a transitionelement, and 0≦x≦1 and 0≦y≦2.
 3. The lithium secondary battery accordingto claim 1, wherein said electrolyte solute is selected from the groupconsisting of LiPF₆, LiBF₄, LiClO₄, LiCF₃ SO₃, LiC₄ F₉ SO₃, LiN(CF₃SO₂)₂ and LiAsF₆.
 4. A lithium secondary battery comprising:a negativeelectrode composed mainly of a carbon material consisting essentially ofa graphite having(a) a d-value of the lattice plane (002) obtained byx-ray diffraction thereof of 3.354 to 3.370, (b) a crystallite size inthe c-axis direction obtained by x-ray diffraction thereof of at least200 Å and (c) an average particle diameter of 1 μm to 30 μm; a positiveelectrode composed mainly of a compound capable of occluding anddischarging lithium and which is different from the graphite of thenegative electrode; a separator between said positive electrode and saidnegative electrode; and an electrolyte solution of an electrolyte solutedissolved in a solvent, said solvent consisting essentially of 20% to80% by volume of ethylene carbonate and 80% to 20% by volume of at leastone of dimethyl carbonate and diethyl carbonate.
 5. The lithiumsecondary battery according to claim 4, wherein said compound capable ofoccluding and discharging lithium is represented by the formula Li_(x)MO₂ or Li_(y) M₂ O₄, wherein M is a transition element, and 0≦x≦1 and0≦y≦2.
 6. The lithium secondary battery according to claim 4, whereinsaid electrolyte solute is selected from the group consisting of LiPF₆,LiBF₄, LiClO₄, LiCF₃ SO₃, LiC₄ F₉ SO₃, LiN(CF₃ SO₂)₂ and LiAsF₆.
 7. Alithium secondary battery comprising:a negative electrode composedmainly of a carbon material consisting essentially of a graphitehaving(a) a d-value of the lattice plane (002) obtained by x-raydiffraction thereof of 3.354 to 3.370, (b) a crystallite size in thec-axis direction obtained by x-ray diffraction thereof of at least 200 Åand (c) a specific surface area of 0.5 m² /g to 50 m² /g; a positiveelectrode composed mainly of a compound capable of occluding anddischarging lithium and which is different from the graphite of thenegative electrode; a separator between said positive electrode and saidnegative electrode; and an electrolyte solution of an electrolyte solutedissolved in a solvent, said solvent consisting essentially of 20% to80% by volume of ethylene carbonate and 80% to 20% by volume of at leastone of dimethyl carbonate and diethyl carbonate.
 8. The lithiumsecondary battery according to claim 7, wherein said compound capable ofoccluding and discharging lithium is represented by the formula Li_(x)MO₂ or Li_(y) M₂ O₄, wherein M is a transition element, and 0≦x≦1 and0≦y≦2.
 9. The lithium secondary battery according to claim 7, whereinsaid electrolyte solute is selected from the group consisting of LiPF₆,LiBF₄, LiClO₄, LiCF₃ SO₃, LiC₄ F₉ SO₃, LiN(CF₃ SO₂)₂ and LiAsF₆.
 10. Alithium secondary battery comprising:a negative electrode composedmainly of a carbon material consisting essentially of a graphitehaving(a) a d-value of the lattice plane (002) obtained by x-raydiffraction thereof of 3.354 to 3.370, (b) a crystallite size in thec-axis direction obtained by x-ray diffraction thereof of at least 200Å, (c) an average particle diameter of 1 μm to 30 μm and (d) a specificsurface area of 0.5 m² /g to 50 m² /g; a positive electrode composedmainly of a compound capable of occluding and discharging lithium andwhich is different from the graphite of the negative electrode; aseparator between said positive electrode and said negative electrode;and an electrolyte solution of an electrolyte solute dissolved in asolvent, said solvent consisting essentially of 20% to 80% by volume ofethylene carbonate and 80% to 20% by volume of at least one of dimethylcarbonate and diethyl carbonate.
 11. The lithium secondary batteryaccording to claim 10, wherein said compound capable of occluding anddischarging lithium is represented by the formula Li_(x) MO₂ or Li_(y)M₂ O₄, wherein M is a transition element, and 0≦x≦1 and 0≦y≦2.
 12. Thelithium secondary battery according to claim 10, wherein saidelectrolyte solute is selected from the group consisting of LiPF₆,LiBF₄, LiClO₄, LiCF₃ SO₃, LiC₄ F₉ SO₃, LiN(CF₃ SO₂)₂ and LiAsF₆.
 13. Thelithium secondary battery according to any one of claims 2, 5, 8 or 11,wherein said compound capable of occluding and discharging lithium isselected from the group consisting of LiCoO₂, LiMnO₂, LiNiO₂, LiCrO₂ andLiMn₂ O₄.
 14. The lithium secondary battery according to any one ofclaims 1, 4, 7 or 10, wherein said d-value is 3.355 or more or less than3.360.
 15. The lithium secondary battery according to any one of claims1, 4, 7 or 10, wherein said d-value is 3.360 or more or less than 3.365.16. The lithium secondary battery according to any one of claims 1, 4, 7or 10, wherein said d-value is 3.365 or more or less than 3.370.
 17. Thelithium secondary battery according to any one of claims 1, 4, 7 or 10,wherein said solvent consists essentially of 20% to 80% by volume ofethylene carbonate and 80% to 20% by volume of dimethyl carbonate. 18.The lithium secondary battery according to any one of claims 1, 4, 7 or10, wherein said crystallite size in the c-axis direction obtained byX-ray diffraction is greater than 220 Å.
 19. The lithium secondarybattery according to any one of claims 2, 3, 5, 6, 8, 9, 11 or 12,wherein said crystallite size in the c-axis direction obtained by X-raydiffraction is greater than 220 Å.
 20. The lithium secondary batteryaccording to claim 13, wherein said crystallite size in the c-axisdirection obtained by X-ray diffraction is greater than 220 Å.
 21. Thelithium secondary battery according to claim 14, wherein saidcrystallite size in the c-axis direction obtained by X-ray diffractionis greater than 220 Å.
 22. The lithium secondary battery according toclaim 15, wherein said crystallite size in the c-axis direction obtainedby X-ray diffraction is greater than 220 Å.
 23. The lithium secondarybattery according to claim 16, wherein said crystallite size in thec-axis direction obtained by X-ray diffraction is greater than 220 Å.24. The lithium secondary battery according to claim 17, wherein saidcrystallite size in the c-axis direction obtained by X-ray diffractionis greater than 220 Å.